1. Field of Invention
The present invention relates to a semiconductor device, in particular, the invention relates to a semiconductor device primarily made of nitride semiconductor materials.
2. Background Art
Semiconductor devices with a type of filed effect transistor (FET) primarily made of nitride semiconductor materials are generally formed by epitaxially growing the nitride semiconductor materials on a substrate. Such a semiconductor device inherently provides a two-dimensional electron gas (2DEG) at interface between a channel layer and a barrier layer, exactly, in the channel layer at the interface against the barrier layer. The 2DEG is conducted by biases applied between a source electrode and a drain electrode and modulated by a signal applied to a gate electrode. A Japanese Paten Application layer open No. JP2011-082552A has discloses an FET including an n-type gallium nitride (GaN) layer on the barrier layer. Another Japanese Patent Application laid open No. JP2008-205392A has disclosed an FET providing a dual passivation layer made of silicon nitride (SiN) with a Si-rich composition and another SiN layer with a stoichiometric composition.
An n-type GaN layer disclosed in the former prior art may enhance the current to voltage (I-V) characteristic of a semiconductor device. However, the conductive GaN layer increases a leak current. While, an SiN film with the Si-rich composition degrades, what is called, the current collapsing because excess Si atoms in the SiN film may extract nitrogen (N) atoms in the GaN layer, in other word, excess Si atoms easily bind with N atoms, which causes vacancies in the GaN layer and accordingly, increasing deep traps.